In the purification of molten metals, particularly aluminum, it is frequently desired to remove dissolved gases such as hydrogen or dissolved metals, chiefly magnesium. The removal of dissolved gas is known as “degassing”, while the removal of magnesium is known as “demagging”.
When demagging or degassing aluminum, chlorine or nitrogen gas, respectively, is released into a quantity of molten aluminum, this quantity generally being referred to as a bath of molten aluminum. The bath is usually contained within the walls of a reverbatory furnace. When demagging aluminum, chlorine gas is released into the bath and the chlorine bonds, or reacts, with the magnesium wherein each pound of magnesium reacts with approximately 2.95 pounds of chlorine to form magnesium chloride, a generally insoluble material which can be skimmed from the surface of the bath. Several methods for introducing chlorine into a molten aluminum bath are known.
A gas injection tube has been used to introduce gas into a molten metal stream where molten metal is pumped from one chamber to another. The gas injection tube is inserted into a hole in the pump base of the molten metal pump either upstream of, downstream of or in the pump chamber. Gas, such as chlorine, is injected into the molten metal stream where it can react with the molten metal.
The pump base of the molten metal pump is one of the more expensive pieces of the pump assembly. Since the gas injection tube is inserted into a hole in the base, it is difficult to retrofit a metal pump that does not include a gas inlet. Also, the more holes that are drilled into the base, the greater the likelihood that the base can wear out more quickly. Accordingly, it is desirable to provide a gas injection tube having a tube base that can be positioned near the outlet of the pump base of the molten metal pump.